The stability and temperature drift of external gain setting resistor R_G also affects gain. The contribution of R_G to gain accuracy and drift is determined from Equation 1. The best gain drift of 5 ppm/℃ (maximum) is achieved when the INA851 uses G = 1 in the input stage, without R_G connected. In this case, gain drift is limited by the mismatch of the temperature coefficient of the integrated resistors in fully differential amplifier A₃. When the output stage is in attenuating gain mode (OUT− shorted to G02− and OUT+ shorted to G02+), both the 1.25-kΩ and the 5-kΩ resistors contribute mismatch, as do the traces between the G02x and OUTx pins. Only the 5-kΩ resistors contribute mismatch when the output stage is in unity gain mode (with G02− and G02+ floating).

At input stage gains greater than 1, gain drift increases as a result of the individual drift of the 3-kΩ resistors in the feedback of A₁ and A₂, relative to the drift of external gain resistor R_G. The low temperature coefficient of the internal feedback resistors improves the overall temperature stability of applications using input-stage gains greater than 1 V/V over alternate solutions. The low resistor values required for high gain make wiring resistance an important consideration. Sockets add to the wiring resistance and contribute additional gain error (such as a possible unstable gain error) at gains of approximately 20 or greater. To maintain stability, avoid parasitic capacitance of more than a few picofarads at the R_G connections. Careful matching of any parasitics on the R_G pins maintains optimal CMRR over frequency.